1. Field of the Invention
This invention relates to compositions and methods for inhibiting oil field scale formation, and more particularly to compositions and methods for inhibiting scale formation in high brine environments.
2. Prior Art
A common problem encountered in industrial activities and activities involving transport of water or transport of aqueous mixtures is the formation of scale on equipment, particularly on the inside surfaces of conduits. Oil field brines, and most commercial water contain a variety of alkaline earth metal cations, such as calcium, barium and strontium, as well as a variety anions such as bicarbonate, carbonate, sulfate, phosphate and silicate. When such ions are present in sufficient concentrations, they tend to combine to form precipitates. Scale, formed by the deposition of any of several types of such precipitates, including calcium carbonate, calcium sulfate and barium sulfate (barite), therefore tends to coat surfaces in contact with water. Buildup of such scale on, for example, the inside surfaces of conduits not only obstructs fluid flow, but also interferes with heat transfer across the surfaces, facilitates corrosion of the surfaces and harbors the growth of bacteria.
Conventionally, scale formation is inhibited by introducing a scale inhibiting composition to the aqueous environment. Various scale inhibiting compositions have been employed to inhibit scale formation, and several such compositions are illustrated in U.S. Pat. No. 4,187,245 to Redmore et al., U.S. Pat. No. 4,234,511 to Backman, and U.S. Pat. Nos. 4,051,110 and 4,080,375 to Quinlan. Scale inhibiting compositions, such as those disclosed in the above-noted patents, have been found useful for inhibiting scale formation in many typical environments. However, they generally have limited solubility in high brine environments, that is, in brines having in excess of about 150 grams of total dissolved solids per liter of brine. Thus, conventional scale inhibitors generally have been found to be substantially less effective in high brine environments, such as those found in certain oil fields in the Rocky Mountains of the United States.